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Thoughts on a Pebble


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Prologue:

Deep in the forest a man sitting on a large stone once heard a voice. “Do you want to hear a story?” The man looked up, and wondered, because nobody was there. “Do you want to hear a story?” repeated the voice. Then the man realized that the voice was coming from the stone where he was sitting on. “What are stories?” questioned the man. “Stories happened long time ago, my stories are like stars, they never fade away.” And the stone narrated one story after another, until the sun reached the horizon. “Enough for today, come tomorrow, and take with you the other people of your village.” The next day, they came, and again the stone narrated stories until sunset. “This are all my stories, remember them and tell them to your children, so they can tell them to their children and so on.” And it was so that all the stories of humankind came into being.” Ancient story by the Seneca-Indians (Toronto, Canada)

It is often said that ancient myths hold a spark of truth in them, and so it is true that a stone, even a pebble found on ground (or – like in Fig.1. – eroding from a moraine and displayed like a natural monument), can tell a fascinating story – if we can understand the hinds and signs impressed on it by its formation and time. The story how humans learned to read rocks is by itself an incredible tale and surprisingly young.

Fig.2. Collection of typical rocks and fossils of the ages of earth – The Layers of Earth pictured as a book – by Y. Fric, dealer of natural products, Prague 1861 (click on the image to enlarge).

Only in 1778 the Swiss naturalist Jean-Andre de Luc in his opus “Letters on Mountains” proposed hesitant a name for a new approach to observe rocks and earth:

I mean here by cosmology only the knowledge of the earth, and not that of the universe. In this sense, “geology” would have been the correct word, but I dare not adopt it, because it is not in common use.

More than 200 years later the obscure science of geology has developed in many branches with many dedicated followers – so as I.

Fig.3. Geologist (on the left) and field assistant.

My name is David Bressan and I’m a freelance geologist based in the Italian province of South Tyrol. I graduated with a project on Rock Glaciers dynamics and hydrology in the Eastern Alps, this phase left a special interest for Quaternary deposits and modern glacial environments. During my research, studying old maps, photographs and reports on the former extent of glaciers, I became interested in history, especially the development of geomorphologic and geological concepts by naturalists and geologists trough time.

In January 2008 I founded a private blog dedicated to the geology and geomorphology of cold environments (http://rockglacier.blogspot.com/), in May 2010 I decided to outsource the sporadic posts about geology history in a own blog (http://historyofgeology.blogspot.com/) – the rest is history and so one day I was asked if I would be interested to blog on Scientific American´s new BLOG-NETWORK.

Living in one of the key areas for the history of geology I try to combine field trips with the historic research done in these regions, accompanied by historic maps and depictions. I will discuss also general geological concepts worldwide or important events, especially in glaciology, seismology, volcanology, stratigraphy and the relationship of society and geology.

Why approach geology through its history? Today concepts of modern geology – like plate tectonic or the stratigraphic order of the layers – are easily accessible, explained and depicted in books or in the internet, but we tend to forget how many setbacks, failures or injustices early researchers experienced and how much audacity was sometimes demanded from them. When the Swiss professor of philosophy Horace-Bénédict de Saussure ascended in 1787 the 4.810m high Mont Blanc in the Alps to explore the rocks on its summit, he was not sure to return back alive. The Scottish Maria Matilda Ogilvie Gordon (1864-1939), one of the first woman to earn PhDs in geology when access to University for women was strictly restricted, had to listen to lectures sitting in a separate room with the doors half-open. Adventurer, mammologist and palaeontologist Roy Chapman Andrews (1884 -1960) started his career by mopping every morning the floors in the taxidermy studio in the American Museum of Natural History in New York. Not only would it be wrong to forget their accomplishments, but by introducing the persons behind the science I hope also to show how geology works and proceeds.

Geology is rooted and influences profoundly other scientific disciplines and researchers. For example it was the study of geology that gave Charles Darwin confidence in his abilities of observation, as he self reminds in an autobiographic note:

It was soon after I began collecting stones, i.e., when 9 or 10, that I distinctly recollect the desire I had of being able to know something about every pebble in front of the hall door–it was my earliest and only geological aspiration at that time.

Geology provided the deep time to explain the changes of earth, but also life itself as observed by biologists. The fossil record, the archive of earth, shows how extinction and radiation of species occur over geologic time.

But geology influenced not only single men or disciplines, but also the history of entire civilizations. Many myths and chronicles tell about terrifying natural catastrophes, volcanic eruptions, earthquakes, landslides – once these events were regarded as the manifestation of the anger of the gods, and still today they can scare and influence societies. But not only destruction, earth provided also the raw material for civilizations: in our entire history the most used material to fabricate tools were simple rocks – for example carefully selected hard stones and pebbles from a river, processed to be useful tools.

Fig.4. Silex – artefact from the site of Ehringsdorf (Germany, ca. 200.000 years, presumably manufactured by Homo neanderthalensis), showing that central Europe was inhabitat by man for more then 400.000 years.

I think that all these consideration and its immediacy makes geology one of the most approachable sciences  -  so welcome to the History of Geology and I hope that with this blog I can show that everybody can go into the field and listen to the stories that a single stone or pebble will tell us.

I would be glad for comments and suggestions on the blog , consider yourself as welcomed guest – however even the best guests should not exploit hospitality. You can also follow me  on twitter @David_Bressan or drop me an E-mail by using the Contact-link in the header of the blog.

David BressanAbout the Author: Freelance geologist dealing with quaternary outcrops interested in the history and the development of geological concepts through time. Follow on Twitter @David_Bressan.

The views expressed are those of the author and are not necessarily those of Scientific American.



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  1. 1. Mythusmage 3:09 am 07/9/2011

    Here’s a puzzlement for you.

    Some weeks past I heard of a geological puzzle, set in eastern North America, under the state of New York. It seems that the upper layers of New York State are made of granite rocks, but the under layers are all basaltic. It would appear as if the deepest layers of the North American Plate are all basalt, while the uppermost plates are granite, and that the North American Plate are actually two distinct plate, one a basaltic plate originating from the Mid Atlantic Ridge’, while the other is a granitic plate with a more complex origin. Is there anything to this?

    Link to this
  2. 2. David_Bressan 4:19 pm 07/12/2011

    Hello, sorry for the delay, I will be more active and punctual from next week onwards.

    It is a very intriguing question, worth an own post, so here I can give only a brief summary as I understand the question. First I have to specify that there is a difference between plates and earth’s crust.

    The actual plates of earth can comprise both rocks of granitic as basaltic composition; the limits of plates are mostly defined by tectonic thrust systems, the Mid Ocean Ridges or Graben-structures, mountain ranges or the position of volcanoes and earthquakes – these borders can shift over time and even new plates can form over time (we see this happening in Africa). Some borders are in fact not well known – for example in Siberia it is not completely clear if there is only one very large plate, comprising Europe and Asia, or if there are more.
    However there is the composition difference between oceanic crust and continental crust, this distribution of these two kinds of crust remain more or less equal over time, because today new continental crust is not formed on earth in significance quantity.

    – in summary: a plate can be completely formed by oceanic crust, completely formed of oceanic crust or comprise both crust types, the borders of a plate are caused mostly by tectonic processes not by its petrology, these borders can shift, became inactive or form new over time.

    As for the state of New York and the north-eastern part of the U.S., this region is mostly characterized by the Appalachian mountain system – a very complex system of folded, thrusted and metamorphosed provinces 800 to 200 million years old – provinces are thought to be former single fragments of continental crust carried on plates, these fragments collided each to another and became connected to the North-American craton (one part of the very first crust of the young earth) forming the mountain range.
    We therefore have a complex succession of fragments of oceanic crust mixed together with continental crust and there were also volcanism and intrusion of granite. This happened because there were over geologic times multiple and various borders of plates between the single fragments. The Appalachian are however older than the actual Ocean Ridge of the Atlantic – they are not connected to the actual borders of the plates.

    I would reformulate the question and answer as this: the Appalachian consists of various provinces, which include continental crust and parts of oceanic crust, of different age and composition which became trusted each on another by changes in the activity and position of plate boundaries. The position of ocean ridges in the Atlantic and the subduction zone of the Pacific Cascade as seen today seem however to confirm that the North American plate is today a large, stable plate with no actually active borders within.

    Link to this

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